August 2021
Intermediate to advanced
450 pages
4h 46m
Chinese
Content preview from 面向对象的思考过程（原书第5版）
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9.3.2 联合
聚合代表你通常只看到了整体，而联合既代表整体，也代表部分。在立体音响系统例子中，各种各样的组件是独立的，通过接插线（连接各种各样组件的线）连接成整体。
我们拿一个传统的桌面计算机系统来举例（如图9.5）。计算机系统是一个整体，而组成部件为显示器、键盘、鼠标和主机。每个部件都是独立的对象，但它们一起表示了整个计算机系统。主机通过键盘、鼠标以及显示器来分配工作。换句话说，主机需要鼠标的服务，而自己本身无须具备提供这种服务的能力。因此主机通过特定的端口和线将鼠标连接起来，从而可以接受单个的鼠标的服务。
图9.5 联合作为独立的服务
聚合和联合
聚合是由其他对象组成的复杂的对象。而当一个对象需要其他对象的服务时则使用联合。
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